The objective of the project is the identification and investigation of calcium transport mechanisms within the lactating mammary cell. Calcium compartmentation within the Golgi vesicles and perhaps other microvesicles of the mammary cell is being studied by cytochemical techniques, by the distribution of electron-dense cations, and by analyzing untreated, frozen-dried thin section. These ultrastructural approaches are being used in conjunction with X-ray microanalysis. Calmodulin is being investigated as a potential regulator of calcium distribution within the mammary cell. Calmodulin levels are correlated with the state of lactogenesis and may stimulate a Ca2 ion -ATPase associated with membranes of the Golgi complex. An in vitro system composed of isolated acini (alveoli) is currently being utilized for the study of calcium uptake at the basolateral membrane, calcium distribution within the cell, and calcium incorporation into secretory products.